libdm: add dm_report_column_headings

Add a function to print column headings regardless of whether they
have already been output. This will be used by dmstats to issue
periodic reminders of the column headings.

This patch removes a check for RH_HEADINGS_PRINTED from
_report_headings that prevents headings being displayed if the flag
is already set; this check is redundant since the only existing
caller (_output_as_columns()) already tests the flag before
calling the function.

libdm/.exported_symbols.DM_1_02_104

@@ -1,3 +1,4 @@
+dm_report_column_headings
 dm_report_get_interval_ms
 dm_report_get_interval_ns
 dm_report_set_interval_ms

libdm/libdevmapper.h

@@ -1896,6 +1896,14 @@ int dm_report_object_is_selected(struct dm_report *rh, void *object, int do_outp
 int dm_report_compact_fields(struct dm_report *rh);
 
 int dm_report_output(struct dm_report *rh);
+
+/*
+ * Output the report headings for a columns-based report, even if they
+ * have already been shown. Useful for repeating reports that wish to
+ * issue a periodic reminder of the column headings.
+ */
+int dm_report_column_headings(struct dm_report *rh);
+
 void dm_report_free(struct dm_report *rh);
 
 /*

libdm/libdm-report.c

@@ -3922,9 +3922,6 @@ static int _report_headings(struct dm_report *rh)
 	char *buf = NULL;
 	size_t buf_size = 0;
 
-	if (rh->flags & RH_HEADINGS_PRINTED)
-		return 1;
-
 	rh->flags |= RH_HEADINGS_PRINTED;
 
 	if (!(rh->flags & DM_REPORT_OUTPUT_HEADINGS))
@@ -3997,6 +3994,11 @@ static int _report_headings(struct dm_report *rh)
 	return 0;
 }
 
+int dm_report_column_headings(struct dm_report *rh)
+{
+	return _report_headings(rh);
+}
+
 /*
  * Sort rows of data
  */

tools/dmsetup.c

@@ -3970,6 +3970,8 @@ doit:
 		r = _perform_command_for_all_repeatable_args(cmd, subcommand, argc, argv, NULL, multiple_devices);
 
 		if (_report) {
+			if (_count > 1)
+				dm_report_column_headings(_report);
 			dm_report_output(_report);
 
 			if (_count > 1) {